Short answer
Back length and curve added at the pattern; the collar re-seats itself.
Why it happens
Upper-back curve shortens the back line.
Why ready-to-wear cannot fix it
Size charts grade uniformly; rounded upper back is a personal geometry. A block adjusted in one place pulls in another — which is why the correction must exist in the pattern, not in the fitting-room mirror.
How the house drafts for it
Back length and curve added at the pattern; the collar re-seats itself. The correction is recorded in your Fit Passport, so every later commission starts from it automatically.
Where it matters most
This correction carries most for: suit, overcoat, shirt. It is reviewed at every fitting, in every city, for every garment.
Fit Library entry 36 of 48 · Reviewed by Bonturberg Editorial Review · 2026-09-08